The overall objective of this research proposal is to study, on the cellular and animal level, two of the extracellular products of Pseudomonas aeruginosa which are known to contribute to the virulence of the organism. 1) On the cellular level, to compare the entry and subsequent processing of pseudomonas toxin by sensitive and resistant mammalian cells. Biochemical and electron microscopic studies will be compared to determine if toxin enters by receptor mediated endocytosis and is processed by lysosomes, before inactivating its cytoplasmic target, elongation factor 2. 2) In a burned mouse model, to characterize further contribution of bacterial proteolytic enzymes and toxin to the pathogenesis of P. aeruginosa infections. Virulence of mutant strains of P. aeruginosa with different proteolytic enzyme and toxin producing capabilities will be assessed. The effect of proteolytic enzymes on the spread of toxin and bacteria from the burn site will be determined. 3) To develop prophylactic and therapeutic regimen which will block activity of the two putative virulence factors and to see if these regimens will reduce severity of infection with P. aeruginosa. Protection by active and passive immunization against Pseudomonas infections will be measured. Mean time to death, bacterial quantitations of liver and skin effect on functional liver elongation factor 2 will be determined.